The present invention relates to an apparatus for producing a tube with successive corrugations of substantially uniform configuration and wall thickness from a tubular blank of constant diameter.
The DE-AS 13 03 671 discloses an apparatus for continuous production of annular corrugations on a tubular blank of constant diameter. This apparatus comprises a stationarily mounted vertically arranged core pin which is provided with an axially extending hollow section for guiding a multiple part tube mandrel as well as a piston-like enlargement at the free end of the shaft section, which forms an abutment for radially movable, hydraulically operated holding and forming jaws. After pushing a smooth-walled tubular blank onto the core pin, the holding and forming jaws are first moved in engagement with the blank to press the latter against the piston-like enlargement. Subsequently thereto, clamping jaws are pressed by means of radially arranged hydraulically operated cylinder-and-piston units connected with the mandrel against the blank, whereby the mandrel supports the blank inwardly at the region of the clamping jaws. Between the piston-like enlargement, the tubular mandrel and the tubular blank there is now formed an annular expansion space which is impinged by pressure fluid fed into the space through the hollow shaft and a crossbore, so that the wall of the tubular blank bulges outwardly. After the bulge reaches a predetermined dimension, the tubular mandrel together with the clamping jaws and the clamped blank is moved by means of hydraulically operated cylinder-and-piston units arranged parallel to the core pin in direction toward the piston-like enlargement, whereby the tubular wall is expanded and an annular corrugation is formed.
A disadvantage of this known apparatus is the necessary sealing of the expansion space in the region of the piston-like enlargement and that of the tubular mandrel. Sealing rings of elastic material are provided for this purpose, which are axially compressed to thus be radially deformed and pressed against the inner surface of the tubular blank, respectively against the previously produced corrugation. The compression of the seal in the region of the piston-like enlargement and that of the tubular mandrel is produced by cylinder-and-piston systems which are axially displaced by hydraulic fluid. The elastic seals are, during forming of corrugations in the blank, continuously compressed and again released, so that the material will necessarily fatigue, respectively be worn, which will result in leakage, and in addition the cylinder-and-piston units for the compression of the elastic seals have to be properly sealed.
The therewith-connected necessary exact fits and seals considerably increase the manufacturing cost. In addition, increased maintenance cost is necessary in order to assure a proper function of this apparatus. Especially disadvantageous in this known construction is the necessary feeding of the hydraulic fluid to the cylinder-and-piston unit in the multipart tube mandrel. For this purpose, there is provided in the hollow shaft an additional tube. It is also of disadvantage that the cylinder-and-piston unit in the piston-like enlargement is to be supplied with hydraulic pressure fluid. For this purpose an additional conduit is provided at the outer end of the piston-like enlargement. This necessary additional tube will complicate the removal of a finished corrugated tube, as well as the placement of a new tubular blank into the apparatus. An automatic feeding of the blanks is, therefore, impossible. In addition, the known apparatus needs, due to its construction, a large installation space.